U.S. Pat. No. 5,192,156, issued Mar. 9, 1993, discloses apparatus for draining liquid from a surface into a sewer through a passageway extending between the surface and the sewer and for forming a liquid barrier between the sewer and the surface to prevent the flow of gases from a sewer to a surface. The apparatus incorporates structure which facilitates the flow of drainage liquid therethrough.
While the apparatus of U.S. Pat. No. 5,192,156 is highly effective, direct close visual inspection by an individual is required to determine whether or not sufficient liquid is in place in the apparatus to form a gas barrier. To determine whether such is the case, an inspector has to actually observe the interior of a conduit of the apparatus, either through holes in a grating at the top of the conduit or by removing the grating and directly viewing the conduit interior.